Hull and propeller arrangement

ABSTRACT

Hull and propeller arrangement for a surface watercraft ( 1 ), provided with at least one propeller ( 3 ), in addition to which the propeller ( 3 ), at high speeds of the watercraft, is surface-piercing, and the propeller ( 3 ) is arranged in such a manner that only the propeller blades ( 11 ) or parts thereof are submerged in the water at high speeds of the watercraft ( 1 ), in addition to which the hull ( 2 ) is provided with at least one streamlined projecting part ( 4 ) extends essentially in the longitudinal direction of the hull ( 2 ), the projecting part ( 4 ), in terms of its outer shape, has, at its aft end ( 6 ), an end edge ( 15 ) which, at least in part, extends essentially transversely to the longitudinal direction of the projecting part ( 4 ), the propeller ( 3 ) is locaded immediately astern of the end edge ( 15 ), and a part of the propeller, in the radial direction, extends beyond the delimiting surfaces of the projecting part ( 4 ). Each projecting part ( 4 ) is arranged in such a manner that, at high speeds of the watercraft ( 1 ), a bearing area ( 8 ) for the watercraft ( 1 ) is formed, which consists essentially of a part of the surface of the projecting part ( 4 ), which is situated immediately forward of the end edge ( 15 ) and on the very bottom of the projecting part ( 4 ).

This application is the US national application of internationalapplication PCT/SE01/01010 filed 09 May 2001, which designated the US.

TECHNICAL FIELD

The present invention relates to a hull and propeller arrangement.

PRIOR ART

Surface-piercing propellers, that is to say propellers of which theblades, while the boat is underway at high speeds, are situatedalternately in a position above the water and in a position below thewater while the propeller rotates, are well known for surfacewatercraft, in particular fast motor boats. Surface-piercing propellersmake it possible, for a given hull and a given shaft horsepower, todrive a boat at considerably higher speeds than fully submergedpropellers. This improved performance in the case of surface-piercingpropellers is due to the fact that the resistance associated withconverting the rotational power of the power source into a propellingforce for the hull is considerably smaller than in the case ofconventional, fully submerged propellers.

In order to reduce the hydrodynamic resistance, it is desirable that asfew parts as possible are in the water while the boat is underway. Asfar as the propulsion arrangement of the boat is concerned, this desireis satisfied to a great extent if parts which do not contribute to thedirect power transmission to the water are situated outside the waterflow. As far as propellers are concerned, this is achieved if only thepropeller blades come into contact with the water and the propeller hubis situated above the surface of the water.

American U.S. Pat. No. 3,793,980 describes a system withsurface-piercing propellers by means of which, in a controlled manner,the propeller hub is, at high speeds, situated outside the water flow,and only the propeller blades come into contact with the water.

When a boat planes, the hull acts on the water with a force whichpresses the water downwards, the hull being supported by the water bymeans of an opposite force, so that the contact area between the hulland the water is smaller than when the boat travels at displacementspeed. At very high speeds, the contact area is relatively very smalland is situated furthest astern on the hull. If the hull is designed soas to have a number of contact areas when it planes, at least one ofthem is situated furthest astern on the hull. If the movement of theboat is subjected to disruption, caused for example by the boat runningover a wave on the surface of the water, with a subsequent rotationalmovement in the pitching direction, the centre of rotation is oftenlocated close to the aft contact area between the hull and the water.This movement results in a surface-piercing propeller, which is locatedat a certain distance in the longitudinal direction from the aft contactarea, moving essentially upwards or downwards. This in turn means that,during the movement, the size of that part of the propeller which issituated in the water changes. At times, the propeller can be liftedcompletely out of the water. The vertical movement of the propeller inrelation to the surface of the water leads to disruption of thepropulsion of the boat and poor utilization of the propulsion resourcesof the boat.

When a boat provided with a conventional surface-piercing propellerarrangement travels at relatively low speed just above the speed rangefor transition between displacement propulsion and planing propulsion,the level of the surface of the water in relation to the hull is raisedimmediately astern of the hull. This means that a propeller located inthis region is surrounded by water at this speed and loses itssurface-piercing operating mode. At the displacement speed of the boat,the propeller also loses its surface-piercing operating mode.

In conventional motor boats, the propeller, or each propeller, islocated at a certain distance from the drive shaft leadthrough, that isto say the place in which the drive shaft extends from inside the hullto its outside. In order to fix the propeller in the radial direction,the drive arrangement is therefore usually provided, immediately next tothe propeller, with a bearing which is fastened to a structure, forexample in the form of a bearing bracket, which is in turn fastened tothe hull. The drive arrangement thus has to be mounted both at the driveshaft leadthrough and next to the propeller. This conventionalarrangement with a bearing for the propeller and associated fasteningstructures requires the use of a plurality of construction parts and, oncontact with the water flow, constitutes a source of resistance duringpropulsion.

THE OBJECT OF THE INVENTION

One object of the invention is to provide a hull and propellerarrangement for a surface watercraft, which reduces disruption of thepropulsion of the boat.

Another object of the invention is to provide a hull and propellerarrangement for a surface watercraft which reduces resistance duringpropulsion of the boat.

A further object of the invention is to provide a hull and propellerarrangement for a surface watercraft, which affords efficient propulsionin a greater speed range than conventional hull and propellerarrangements.

A further object of the invention is to provide a hull and propellerarrangement for a surface watercraft, which simplifies mounting of thedrive arrangement for each propeller.

DESCRIPTION OF THE INVENTION

The position of each propeller immediately astern of an end edge on theaft end of a part projecting from the hull means that the propeller islocated close to a surface which, at high speeds, is a bearing surface,which in turn means that rotational movements in the pitching directionof the boat, caused for example by the boat running into waves, willresult in only small vertical movements of the propeller. This in turnresults in the movements of the propeller blades in relation to thesurface of the water being small, and any disruption of the propulsionof the boat is thus small.

The position of each propeller immediately astern of the respective endedge on the aft end of the respective projecting part also means thatessentially only the blades of the propeller come into contact with thewater flow, even at relatively low speeds when the boat is just abovethe speed range for transition between displacement mode and planingmode.

According to one embodiment, the propeller is, by virtue of its size andpositioning, surface-piercing at displacement speeds, at least atrelatively high displacement speeds.

According to the invention, each propeller is provided with a hub which,at the junction between an aft delimiting surface and a peripheraldelimiting surface, is designed with a relatively sharp hub edge. Thishub edge makes possible effective separation of the water flow from thepropeller.

The end edge on each projecting part makes possible effective separationof the water flow from the projecting part.

In the vicinity of the propeller, the projecting part has a crosssection which, at least in part, is essentially shaped like a part of acircle, the centre of which in the radial direction essentiallycoincides with the centre of the propeller. The radius of said circle isessentially the same as the radius of an imaginary circle which, onrotation of the propeller, is generated by the region where thepropeller blades meet the propeller hub. The result of this is that, ina controlled manner, the surface of the water flowing past, which hasleft the projecting part, essentially meets the periphery of thepropeller hub.

According to the invention, the leadthrough of the drive shaft throughthe hull is located immediately next to the propeller hub, whichsimplifies mounting of the propeller because it eliminates therequirement for the arrangement to have an additional bearing with anassociated fastening structure outside the hull.

DESCRIPTION OF THE FIGURES

In the drawing:

FIG. 1 shows a perspective view from the side and to some extent frombelow of a motor boat provided with a hull and propeller arrangementaccording to the invention;

FIG. 2 shows a perspective view obliquely from the stern and to someextent from below of a motor boat provided with a hull and propellerarrangement according to the invention;

FIG. 3 shows a perspective view from the stern and to some extent frombelow of a motor boat provided with a hull and propeller arrangementaccording to the invention;

FIG. 4 shows an enlarged view of the aft part of a motor boat shown inFIG. 1;

FIG. 5 shows a cross section along the line V—V in FIG. 3 of a hull andpropeller arrangement according to the invention, and

FIG. 6 shows a cross section along the line V—V in FIG. 3 of a hull andpropeller arrangement according to the invention.

PREFERRED EMBODIMENT

FIG. 1 shows a motor boat 1 with a hull 2 and two propellers 3. The twopropellers 3, which are surface-piercing and counter-rotating and thedrive shafts of which extend essentially forwards in the longitudinaldirection of the boat 1. The hull 2 is provided with two projectingparts 4. Each projecting part 4 is streamlined and extends in thelongitudinal direction of the hull 2. Each projecting part 4 has, at afront end 5, a shape which merges in a streamlined manner with the shapeof the hull 2. Each front end 5 is, in the longitudinal direction,located approximately in the centre of the hull 2 and, in the transversedirection, between the centre of the hull 2 and its edge. Eachprojecting part 4 extends to an aft end 6 which is forward of and veryclose to one of the propellers 3. On its front part, the hull 2 isshaped with a belly 7 where the hull 2 is deeper than in most otherplaces.

Reference is now made to FIG. 2. At high speeds, the boat 1 is supportedby the water flowing past on relatively small bearing areas. In thisconnection, bearing area means an area on the hull 2, which is in directcontact with the water flowing past, and on which forces act, which liftthe hull 2 up. At high speeds, two aft bearing areas 8 are formed on theboat 1 in this exemplary embodiment, which are indicated by the linedareas in FIG. 2 and each consist of that part of the surface of eachprojecting part 4 which extends from the aft end 6 and forward arelatively short distance. A forward bearing area is formed on the belly7.

In FIG. 3, it can be seen that each propeller 3 is designed with arelatively large hub 9 which is in turn designed essentially as acircular plate.

FIG. 4 shows that the hub 9 has, at its periphery, a peripheraldelimiting surface 10 which forms a cylinder, the length of whichessentially corresponds to the thickness of the plate which forms thehub 9. A number of propeller blades 11, in this embodiment sixteen,extend in the radial direction from the peripheral delimiting surface10.

FIG. 5 shows that the hub 9 has an aft delimiting surface 12 whichextends essentially in the radial direction and is orientatedessentially at right angles to the peripheral delimiting surface 10. Atthe junction between the aft delimiting surface 12 and the peripheraldelimiting surface 10, a relatively sharp hub edge 13 is formed. Thishub edge 13 makes possible effective separation of the water flow fromthe propeller 3.

The cross section of each projecting part 4 is, at least at the aft end6, essentially part-circular. Close to the aft end 6, the radius of thecross section corresponds essentially to the outer radius of the hub 9,and the centre of the circle defined by the cross section essentiallycoincides in the radial direction with the centre of the propeller. Atthe aft end 6, each projecting part 4 forms an end surface 14 which isessentially parallel to the propeller disc. At the junction between theend surface 14 and the external surface immediately forward of the endsurface 14, a relatively sharp end edge 15 is formed. This end edge 15makes possible effective separation of the water flow from theprojecting part 4. The distance between the end edge 15 and thepropeller 3 is minimized, taking account of what is practicallypossible. In any case, it is considerably smaller than the length ofeach propeller blade 11.

FIG. 6 illustrates one effect of the propulsion arrangement according tothe invention. The water flow is illustrated by lines below the boat 1.As the radius of the cross section of the projecting part 4 close to theaft end 6 essentially corresponds to the outer radius of the hub 9, andthe propeller 3 is located immediately astern of the aft end 6, thesurface of the water flow lies, at high speeds, in the region where thepropeller blades 11 meet the peripheral delimiting surface 10 of the hub9.

If, at high speeds, pitching movements of the boat 1 occur, caused forexample by the boat 1 running into waves, the rotation will take placeessentially about a horizontal axis in the transverse direction locatedin the regions of the aft bearing areas 8. As each propeller 3 islocated immediately astern of the respective aft bearing area 8, andthus close to the centre of rotation, said rotational movements willresult in only small vertical movements of the propeller 3.

FIG. 5 shows how a part of the propeller 3 is located in a recess 16 inthe hull 2. According to the invention, the leadthrough 18 of the driveshaft 17 through the hull 2 is located immediately next to the propellerhub 9, which simplifies mounting of the propeller 3 because iteliminates the requirement for the arrangement to have an additionalbearing with an associated fastening structure outside the hull 2.

The positioning of each propeller 3 immediately behind the respectiveprojecting part 4 and its vertical positioning result in the propellerbeing surface-piercing even at at least relatively high displacementspeeds of the boat 1. The fact that each propeller 3 is relatively largealso contributes to this.

The motor boat 1 in the embodiment described is provided with twopropellers 3 located at a distance from one another in the transversedirection of the hull 2. These are arranged in such a manner that, whilethe motor boat 1 is underway, the pitch angle of the propeller blades 11can be adjusted for each propeller 3 individually. As a result, steeringof the boat 1 can be carried out without a rudder. The absence of arudder reduces the number of parts which are in contact with the waterwhile the boat 1 is underway and in this way reduces the resistanceduring propulsion of the boat 1.

The blades 11 on each propeller 3 are preferably arranged in such amanner that the pitch angle can be adjusted while underway in order toallow it to be adapted to the speed at which the boat is travelling,which in turn means more effective utilization of the propulsionresources of the boat 1.

1. A surface watercraft, comprising: a hull; two propellers which, athigh speeds of the watercraft, are water surface-piercing, saidpropellers being such that only the propeller blade or parts thereof aresubmerged in the water at high speeds of the watercraft; said hullhaving a belly and two streamlined projecting parts, said projectingparts extending in a longitudinal direction of the hull; each projectingpart in terms of its outer shape, having at its aft end, an end edgewhich, at least in part, extends generally transversely to thelongitudinal direction of the projecting part; each propeller beinglocated immediately astern of the respective end edge and a part of eachpropeller, in the radial direction, extending beyond the delimitingsurfaces of the respective projecting part; and said projecting partshaving arranged at high speeds of the watercraft, an aft bearing areaformed on each projecting part, each aft bearing area consisting of apart of the surface of the respective projecting part locatedimmediately forward of said end edge and on the bottom of the projectingpart; and a forward bearing area formed on the belly of the hull,whereby the watercraft is supported by the water flowing past thebearing areas on which forces act to lift the hull up.
 2. A watercraftaccording to claim 1 wherein each projecting part has, adjacent therespective propeller, a cross section which, at least in part, is shapedlike part of a circle, in that the center of this circle, adjacent thepropeller, substantially coincides in a radial direction with the centerof the propeller, and wherein the radius of this circle adjacent thepropeller is smaller than the radius of the periphery of the propeller.3. A watercraft according to claim 2 wherein the radius of the circlewhich is formed by the cross section of the projecting part adjacent thepropeller is substantially the same as the radius of an imaginary circlewhich, on rotation of the propeller, is generated at the juncture of thepropeller blades and the propeller hub.
 4. A watercraft according to 1wherein each propeller has, in relation to the propeller blades, arelatively large hub, said hub having at its periphery, a peripheraldelimiting surface which is shaped substantially like a cylinder, saidhub having an aft delimiting surface, and the junction between the aftdelimiting surface and the peripheral delimiting surface having a sharphub edge.
 5. A watercraft according to claim 1 wherein the propellersare located at a distance from one another in the transverse directionof the hull, and arranged in such a manner that, while the watercraft isunderway, the pitch angle of the propeller blades can be adjustedindividually for each propeller.
 6. A watercraft according to claim 1wherein a leadthrough of a drive shaft through the hull and mounting thepropellers is located immediately adjacent the propeller hub.
 7. Awatercraft according to claim 1 wherein said belly lies generallyforwardly of the projecting parts and along a centerline, said aftbearing areas of the projecting parts being located forwardly of thepropellers, said propellers being located forwardly of the aft end ofthe watercraft.
 8. A watercraft according to claim 7 wherein saidprojecting parts include an upwardly extending recess between said partslying generally along the centerline of the watercraft.